Radio channel control method and receiving apparatus

ABSTRACT

A base station used in a radio communication system includes a transmitting unit operable to transmit a signal to a receiver and a receiving unit operable to receive control signals indicating a changing in transmission power and another transmission parameter of the base station from the receiver which generates the control signals by measuring reception condition for a specific signal transmitted from the base station.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 11/043,307,filed Jan. 26, 2005, which is a U.S. continuation application filedunder 35 USC 111 (a) claiming benefit under 35 USC 120 and 365 (c) ofPCT application JP03/01881, filed Feb. 20, 2003. The foregoingapplications are hereby incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a radio channel control method for, ina mobile communication system having a transmitting apparatus and areceiving apparatus, controlling a radio channel from the transmittingapparatus toward the receiving apparatus, and to the receiving apparatusfor which the radio channel control method is applied.

BACKGROUND ART

In radio communication, in particular in a mobile communication, a radiochannel set between communication apparatuses which carry outinformation transmission/reception is likely to fluctuate. In order tocarry out information transmission using such a radio channelappropriately, transmission parameters of the radio channel isappropriately changed. The transmission parameters include, for example,a modulation method, a coding rate, a ratio of the number of true,information bits with respect to the number of total transmission bitsincluding redundancy bits, such as error correction bits (referred to asa ‘Rate-Matching ratio’, hereinafter) or the number of spreading codesused in a CDMA (Code Division Multiple Access) communication.

FIG. 1 shows a configuration example in the prior art of a mobilecommunication system changing the transmission parameters of the radiochannel. The mobile transmission system shown in the figure includes abase station 500 acting as a transmitting apparatus and a mobile station600 acting as a receiving apparatus. Hereinafter, it is assumed that, asthe transmission parameters, a coding rate and a modulation method areapplied.

The base station 500 includes an encoder 502, a modulation, part 504, atransmission part 506, a circulator 508, an antenna 510, a receptionpart 512, a demodulation part 514, a decoder 516 and a transmissionparameter setting part 518. On the other hand, the mobile station 600includes an antenna 602, a circulator 604, a reception part 606, ademodulation part 608, a decoder 610, a block error rate deriving part612, a transmission parameter determination part 614, a transmissionbaseband part 616 and a transmission part 618.

Change of the transmission parameters of the radio channel from the basestation 500 toward the mobile station 600 (referred to as a ‘downlinkradio channel’, hereinafter) is carried out in the following procedure.That is, based on the coding rate used as the transmission parameternotified of by the transmission parameter setting part 518, the encoder502 of the base station 500 encodes input data to be transmitted, andoutputs it to the modulation part 504. Based on the modulation methodnotified of by the transmission parameter setting part 518, themodulation part 504 modulates a baseband signal with the data encoded(referred to as ‘encoded data’, hereafter), and outputs it as a signalto be transmitted to the transmission part 506. The transmission part506 transmits the signal modulated by the encoded data, to the mobilestation 600, via the circulator 508 and the antenna 510.

The reception part 606 in the mobile station 600 receives the signalfrom the base station 500 via the antenna 602 and the circulator 604,and outputs it to the demodulation part 608. The demodulation part 608applies the modulation method corresponding to the modulation methodapplied by the modulation part 504 of the base station 500, demodulatesthe input signal, and outputs the encoded data to the decoder 610. Thedecoder 610 applies a decoding method corresponding to an encodingmethod applied by the encoder 502 of the base station 500, decodes theinput encoded data, and outputs the data obtained from the decoding. Theblock error rate deriving part 612 monitors the decoding of the decoder610, derives a data error rate per a block which is a predeterminedtransmission unit (referred to as a ‘block error rate’, hereinafter),and outputs the same to the transmission parameter determination part614.

Based on the block error rate, the transmission parameter determinationpart 614 determines the coding rate and the modulation method which arethe transmission parameters. Specifically, the transmission parameterdetermination part 614 determines that a propagation environment of thedownlink radio channel is bad in a case where the block error rate ishigh, that is, the data error rate is high, and, changes the coding rateto a smaller one, or changes the modulation method into one applyinglarger transmission energy per bit. On the other hand, the transmissionparameter determination part 614 determines that the propagationenvironment of the downlink radio channel is good in a case where theblock error rate is low, that is, the data error rate is low, and,changes the coding rate to a larger one, or changes the modulationmethod into one applying smaller transmission energy per bit. Further,the transmission parameter determination part 614 outputs informationconcerning the new transmission parameters to the transmission basebandpart 616.

The transmission baseband part 616 encodes the information concerningthe new transmission parameters, and further, modulates a basebandsignal of an uplink direction toward the base station 500 (referred toas an ‘uplink baseband signal’, hereinafter) by the informationconcerning the new transmission parameters, and outputs the same to thetransmission part 618. The transmission part 618 outputs the inputsignal to the base station 500 via the circulator 604 and the antenna602.

The reception part 508 of the base station 500 receives the signal fromthe mobile station 600 via the antenna 510 and the circulator 508, andoutputs the same to the demodulation part 514. The demodulator 514demodulates the input signal, and outputs the encoded data,to thedecoder 516. The decoder 516 decodes the input encoded data, and outputsthe information concerning the transmission parameters obtained from thedecoding, to the transmission parameter setting part 518.

The transmission parameter setting part 518 recognizes the new codingrate and modulation method based on the input information concerning thetransmission parameters. Further, the transmission parameter settingpart 518 notifies the encoder 502 of the coding rate, and notifies themodulation part 504 of the modulation method. In data transmissioncarried out after that from the base station 500 toward the mobilestation 600, the encoder 502 applies the new coding rate, and themodulation part 504 applies the new modulation method.

As to the prior arts relating to the above-described transmissionparameters, see the following patent documents 1 through 4, for example:

(Patent Document 1)

Japanese Laid-open Patent Application No. 2001-238256;

(Patent Document 2)

Japanese Laid-open Patent Application No. 2001-339458;

(Patent Document 3)

Japanese Laid-open Patent Application No. 2002-84578; and

(Patent Document 4)

Japanese Laid-open Patent Application No. 11-88940.

However, in the above-described method of changing the transmissionparameters, a time is required for deriving the block error rate bymeans of the block error rate deriving part 612. Thereby, the basestation 500 cannot change the transmission parameters rapidly inresponse to a fluctuation of the propagation environment of the downlinkradio channel.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a radio channel controlmethod and a receiving apparatus solving the above-mentioned problem, bywhich it is possible to rapidly respond to a fluctuation of apropagation environment of a radio channel.

In order to achieve this object, in a mobile communication system havinga transmitting apparatus and a receiving apparatus according to thepresent invention, in a radio channel control method for controlling aradio channel from the transmitting apparatus toward the receivingapparatus, the receiving apparatus generates transmission power controlinformation for controlling transmission power of the radio channelaccording to a propagation environment of the radio channel; generatesinformation concerning a transmission parameter based on thetransmission power control information; and notifies the transmittingapparatus of the information concerning the transmission parameter; andthe transmitting apparatus controls the radio channel based on theinformation concerning the transmission parameter received from thereceiving apparatus.

By this radio channel control method, the receiving apparatus generatesthe information concerning the transmission parameter based on thetransmission power control information for controlling the transmissionpower of the radio channel. Thus, unlike the prior art, it is notnecessary to use the block error rate for generating the informationconcerning the transmission parameter. Thereby, the transmittingapparatus can change the transmission parameter rapidly in response to afluctuation of the propagation environment of the radio channel.

BRIEF DESCRIPTION OF DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from reading the following detailed descriptionwith reference to accompanying documents.

FIG. 1 shows a configuration example of a mobile communication system inthe prior art;

FIG. 2 shows a configuration example of a mobile communication system ina first embodiment of the present invention;

FIG. 3 shows a correspondence relationship between transmissionparameters and transmission parameter concerned information;

FIG. 4 shows a configuration example of a mobile communication system ina second embodiment of the present invention;

FIG. 5 shows a configuration example of a mobile communication system ina third embodiment of the present invention;

FIG. 6 shows a configuration example of a mobile communication system ina fourth embodiment of the present invention;

FIG. 7 shows a configuration example of a mobile communication system ina fifth embodiment of the present invention;

FIG. 8 shows a configuration example of a mobile communication system ina sixth embodiment of the present invention;

FIG. 9 shows a configuration example of a mobile communication system ina seventh embodiment of the present invention;

FIG. 10 shows a configuration example of a mobile communication systemin an eighth embodiment of the present invention; and

FIG. 11 shows a configuration example of a mobile communication systemin a ninth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE PRESENT INVENTION

Embodiments of the present invention are described below with referenceto figures.

FIG. 2 shows a configuration example of a mobile communication systemaccording to a first embodiment of the present invention. The mobilecommunication system shown in FIG. 2 includes a base station 100 actingas a transmitting apparatus and a mobile station 200 acting as areceiving station. This mobile communication system appropriatelychanges transmission parameters in response to a fluctuation of apropagation environment of a radio channel (downlink radio channel)toward the mobile station 200 from the base station 100. Hereinafter, itis assumed that, as the transmission parameters, a coding rate and amodulation method are applied.

The base station 100 includes an encoder 102, a modulation part 104, atransmission part 106, a circulator 108, an antenna 110, a receptionpart 112, a demodulation part 114, a decoder 116 and a transmissionparameter setting part 118. The mobile station 200 includes an antenna202, a circulator 204, a reception part 206, a demodulation part 208, adecoder 210, a TPC bit generation part 212, a transmission parameterdetermination part 214, a transmission baseband part 216 and atransmission part 218.

Change of the transmission parameters of the downlink radio channel fromthe base station 100 toward the mobile station 200 is carried out by thefollowing procedures. That is, based on the coding rate which is thetransmission parameter notified of from the transmission parametersetting part 118, the encoder 102 of the base station 100 encodes inputdata to be transmitted. Further, the encoder 102 outputs the encodeddata obtained from the encoding to the modulation part 104. Themodulation part 104 demodulates a base band signal with the encoded databased on the modulation method notified of by the transmission parametersetting part 118, and outputs it to the transmission part 106.

The transmission part 106 outputs a signal, modulated with the encodeddata as a signal to be transmitted to the circulator 108. The circulator108 transmits the signal from the transmission part 106, via the antenna110 at predetermined periods, while it outputs a signal received via theantenna 110 to the receiving part 112. The circulator 108 transmits thesignal to be transmitted, toward the mobile station 200 at predeterminedtiming, in this case.

The same as the circulator 108 of the base station 100, the circulator204 of the mobile station 200 transmits a signal from the transmissionpart 218, at predetermined periods via the antenna 202, while it outputsa signal received via the antenna 202, to the reception part 206. Thecirculator 204 in this case outputs the signal which the antenna 202receives from the base station 100, to the reception part 206.

The demodulation part 208 applies a demodulation method corresponding tothe modulation method applied by the modulation part 104 of the basestation 100, and demodulates the input signal. Further, the demodulationpart 208 outputs the thus-obtained encoded data to the decoder 210. Thedecoder 210 applies a decoding method corresponding to the encodingmethod applied by the encoder 102 of the base station 100, decodes theinput encoded data, and outputs data obtained from the decoding.

Further, the demodulation part 208 measures a signal-to-noise powerratio (referred to as an ‘SIR’, hereinafter) of the downlink radiochannel based on the input signal, and outputs the thus-obtained SIR tothe TPC bit generation part 212.

The TPC bit generation part 212 compares the input SIR with apredetermined reference value, and, based on the comparison result,generates a bit (referred to as a ‘TPC bit‘, hereinafter) for orderingthe base station 100 to increase or decrease of transmission power ofthe downlink radio channel. Specifically, the TPC bit generation part212 generates the TPC bit ‘0’ for ordering the base station 100 toincrease the transmission power in a case where the SIR is less than thereference value since the propagation environment of the downlink radiochannel is bad, while, the TPC bit generation part 212 generates the TPCbit ‘1’ for ordering the base station 100 to decrease the transmissionpower in a case where the SIR is equal to or higher than the referencevalue since the propagation environment of the downlink radio channel isgood. Further, the TPC bit generation part 212 outputs the generated TPCbit to the transmission parameter determination part 214.

The downlink radio channel for which the signal-to-noise power ratio ismeasured and also for which the transmission power control is carriedout maybe a radio channel other than the downlink radio channel forwhich the transmission parameter control is carried out. For example, ina mobile communication system applying W-CDMA (Wideband Code DivisionMultiple Access), a DPCH (Dedicated Physical Channel) may be determinedas the downlink radio channel for which the signal-to-noise power ratiomeasurement is carried out and for which the transmission power controlis carried out, while a HS-DPCH (High-Speed Dedicated Physical Channel)may be determined as the downlink radio channel for the whichtransmission parameter control is carried out.

The transmission parameter determination part 214 determines the codingratio and the modulation method which are the transmission parameters,based on the input TPC bit. FIG. 3 shows a relationship betweentransmission parameter values and the transmission parameters(modulation method and coding rate). In FIG. 3, as the transmissionparameter value increases, the transmission parameters correspondingthereto become those by which a communication quality can be ensuredeven for a case where the propagation environment is bad.

When the input TPC bit is ‘0’, that is, for a case where the propagationenvironment of the downlink radio channel is bad and the transmissionpower of the downlink radio channel is to be increased, the transmissionparameter determination part 214 increases the transmission parametervalue corresponding to the transmission parameters, currently applied bythe base station 100 so as to change the coding rate into a smaller oneor change the modulation method into one which applies larger energy perbit, and determines the transmission parameters corresponding to thethus-increased transmission parameter value as new transmissionparameters. On the other hand, when the input TPC bit is ‘1’, that is,for a case where, the propagation environment of the downlink radiochannel is good and the transmission power of the downlink radio channelis to lowered, the transmission parameter determination part 214decreases the transmission parameter value corresponding to thetransmission parameters currently applied by the base station 100 so asto change the coding rate into a larger one or change the modulationmethod into one which applies smaller energy per bit, and determines thetransmission parameters corresponding to the thus-lowered transmissionparameter value as new transmission parameters.

For example, it is assumed that the modulation method currently appliedby the base station 100 is QPSK and the coding rate is ¾. In this case,the transmission parameter value ‘2’ corresponds to these transmissionparameters, according to FIG. 3. The transmission parameterdetermination part 214 increases the transmission parameter value by 1into ‘3’ when the input TPC bit is ‘0’, and determines the transmissionparameters (the modulation method is 16 QAM, and the coding rate is ½)corresponding to the transmission parameter value ‘3’, as newtransmission parameters. On the other hand, the transmission parameterdetermination part 214 decreases the transmission parameter value, by 1into ‘1’ when the input TPC bit is 1’, and determines the transmissionparameters (the modulation method is QPSK, and the coding rate is ½)corresponding to the transmission parameter value ‘1’ as newtransmission parameters. The transmission parameter determination part214 outputs the transmission prater value corresponding to the newtransmission parameters to the transmission baseband determination part216.

The transmission baseband part 216 encodes the transmission parametervalue, modulates the baseband signal toward the base station 200 by thethus-encoded transmission parameter value, and outputs it to thetransmission part 218. The transmission part 218 then outputs the inputsignal to the circulator 204. The circulator 204 transmits the signal tobe transmitted, at predetermined timing to the base station 100 via theantenna 202.

The circulator 108 of the base station 100 outputs the signal receivedfrom the mobile station 200 via the antenna 110 to the reception part112. The reception part 112 outputs this signal to the demodulation part114. The demodulation part 114 demodulates the input signal, and outputsthe encoded data to the decoder 116. The decoder 116 decodes the inputencoded data, and outputs the transmission parameter value thus obtainedfrom the decoding to the transmission parameter setting part 118.

The transmission parameter setting part 118 recognizes the new codingrate and modulation method based on the input transmission parametervalue and the correspondence relationship shown in FIG. 3 between thetransmission parameter value and the transmission parameters. Further,the transmission parameter setting part 118 notifies the encoder 102 ofthe coding rate and notifies the modulation part 104 of the modulationmethod. In data transmission from the base station 100 to the mobile,station 200 after that, the encoder 102 applies the new coding rate andthe modulation part 104 applies the new modulation method.

In the above-described first embodiment, the mobile station 200generates the new transmission parameter value based on the TPC bitcontrolling the downlink radio channel transmission power, and does notneed to apply the block error rate as in the prior art. Thereby, thebase station can change the transmission parameters rapidly in responseto a fluctuation of the downlink radio change propagation environment.

FIG. 4 shows a configuration example of a mobile communication systemaccording to a second embodiment of the present invention. In comparisonto the mobile communication system shown in FIG. 2, the mobile stationof the mobile communication system shown in FIG. 4 additionally includesa majority decision circuit 220 between the TPC bit generation part 212and the transmission parameter determination part 214.

The majority decision circuit 220 determines whether ‘0’ or ‘1’ occursmore in the plurality of TPC bits input from the TPC bit generation part212 during a first predetermined period. Further, the majority decisioncircuit 220 outputs the TPC bit, which is one occurring more, to thetransmission parameter determination part 214. The transmissionparameter determination part 214 determines the coding rate and themodulation method which are the transmission parameters, in the sameprocedures as those in the first embodiment based on the input TPC bit.

It is noted that the majority decision circuit 220 may output, inaddition to the TPC bit which is one occurring more, a differencebetween the number of the TPC bits, which are ones occurring more, andthe number of the TPC bits, which are ones occurring less, to thetransmission parameter determination part 214. In this case, thetransmission parameter determination part 214 increases a changingamount of the transmission parameter value corresponding to thetransmission parameters currently applied by the base station 100, asthe difference becomes larger, and determines the transmissionparameters corresponding to the transmission parameter value, thuschanged by the increased changing amount.

In the second embodiment described above, it is possible to reduce afrequency of transmitting the transmission parameter value to the basestation 100, in comparison to the case of the first embodiment.Accordingly, it is possible to widen a band available for transmittinginformation other than the transmission parameter in the uplink radiochannel from the mobile station 200 toward the base station 100.

FIG. 5 shows a configuration example of a mobile communication systemaccording to a third embodiment of the present invention. In the mobilecommunication system shown in FIG. 5, the mobile station 200 newlyincludes a moving speed detection part 222 between the demodulation part208 and the majority decision circuit 220, in comparison to the mobilecommunication system shown in FIG. 4.

The moving speed detection part 222 detects a moving speed of the mobilestation 200 based on a fluctuation of receiving power of a signal inputto the demodulation part 208. As a specific method of detecting themoving speed, for example, see Japanese Laid-open Patent Application No.6-514586. The moving speed detection part 222 should not necessarilyapply the signal, input to the demotion part 208 to detect the movingspeed of the mobile station 200. For example, any other method, by whichthe moving speed of the mobile station 200 may be detected, may beapplied. For example, a function of a GPS (Global Positioning System) orsuch may be applied. The moving speed detection part 222 outputs thethus-detected moving speed of the mobile station 200, to the majoritydecision circuit 220.

The same as in the second embodiment, the majority decision circuit 220determines which occurs more between ‘0’ or ‘1’ in the plurality of TPCbits input from the TPC bit generation part 212 during the firstpredetermined period. However, when the moving speed of the mobilestation 200 is equal to or more than a predetermined value, since thereis a high possibility that the propagation environment of the downlinkradio channel changes for a large amount during a short period, themajority decision circuit 220 shortens the first predetermined period.Further, when the moving speed of the mobile station 200 is less thanthe predetermined value, since there is a low possibility that thepropagation environment, of the downlink radio channel changes for alarge amount during a short period, the majority decision circuit 220elongates the first predetermined period.

According to the third embodiment described above, the mobile station200 can increase the frequency of transmitting the transmissionparameter value when the moving speed of the mobile station 200 is highand there is a high possibility that the propagation environment of thedownlink radio channel changes for a large amount during a short period,while it can reduce the frequency of transmitting the transmissionparameter value when the moving speed of the mobile station 200 is lowand there is a low possibility that the propagation environment of thedownlink radio channel changes for a large amount during a short period.Thereby, the mobile station 200 can transmit the transmission parametervalue with a suitable frequency in response to the propagationenvironment of the downlink radio channel.

FIG. 6 shows a configuration example of a mobile communication systemaccording to a fourth embodiment of the present invention. In the mobilecommunication system shown in FIG. 6, the mobile station 200 does notincludes the TPC bit generation part 212 between the demodulation part208 and the transmission parameter determination part 213, while newlyincluding a SIR measurement part 224, a reference value setting part226, a comparison part 228 and a majority decision circuit 230, incomparison to the mobile communication system shown in FIG. 2.

According to this fourth embodiment, the demodulation part 208 of themobile station 200 outputs the input signal to the SIR measurement part224. The SIR measurement part 224 measures a signal-to-noise power ratioin the downlink radio channel based on the input signal, and outputs thethus-obtained SIR to the comparison part 228.

In the reference value setting part 226, a reference value of the SIR isset. The comparison part 228 compares the SIR measured by the SIRmeasurement part 224 (referred to as a SIR measurement valuehereinafter) and the SIR reference value set in the reference valuesetting part 226, and outputs a result thereof to the majority decisioncircuit 230.

The majority decision part 230 determines, as to the comparison resultsinput from the comparison part 228 during a second predetermined period,which occurs more between the comparison result indicating that the SIRmeasurement value is more than the SIR reference value and thecomparison result indicating that the SIR measurement value is less thanthe SIR reference value. The majority decision circuit 230 outputs thecomparison result which is one occurring more to the transmissionparameter determination part 214.

The transmission parameter determination part 214 determines the codingrate and the modulation method which are the transmission parametersbased on the input comparison result. Specifically, when the inputcomparison result indicates that the SIR measurement value is more thanthe SIR reference value, the transmission parameter determination part214 changes the coding rate to a larger one or changes the modulationmethod to one applying smaller transmission energy per bit. On the otherhand, when the input comparison result indicates that the SIRmeasurement value is less than the SIR reference value, the transmissionparameter determination part 214 changes the coding rate to a smallerone or changes, the modulation method to one applying largertransmission energy per bit.

The majority decision circuit 230 may output, in addition to thecomparison result which is one occurring more, a difference between thecomparison results which are one occurring more and the comparisonresults which are one occurring less, to the transmission parameterdetermination part 214. In this case, assuming that the relationshipbetween the transmission parameter values and the transmissionparameters is that shown in FIG. 3, the transmission parameterdetermination part 214 increases a changing amount of the transmissionparameter value corresponding to the transmission parameters currentlyapplied by the base station 100 as the difference is larger, and thendetermines the transmission parameters corresponding to the thus-changedtransmission parameter value as new transmission parameters.

In the above-described fourth embodiment, the mobile station 200generates the new transmission parameters based on the SIR of thedownlink radio channel and does not need to apply the block error rateas in the prior art. Therefore the base station 100 can rapidly changethe transmission parameters in response to a fluctuation of thepropagation environment of the downlink radio channel.

FIG. 7 shows a configuration example of a mobile communication systemaccording to a fifth embodiment of the present invention. In the mobilecommunication system shown in FIG. 7, the mobile station 200 newlyincludes a moving speed detection part 232 between the demodulation part208 and the majority decision circuit 230, in comparison to the mobilecommunication system shown in FIG. 6.

The same as the moving speed detection part 222 in the mobile station200 shown in FIG. 5, the moving speed detection part 232 detects amoving speed of the mobile station based on a fluctuation of thereceiving power of the signal input to the demodulation part 208. Themoving speed detection part 232 should detect the moving speed of themobile station 200 with the use of any method, for example, a functionof a GPS or such. The moving speed detection part 232 outputs thethus-detected moving speed of the mobile station 200 to the majoritydecision circuit 230.

The same as in the fourth embodiment, the majority decision circuit 230determines, as to the comparison results input from the comparison part,228 during a second predetermined period, which is one occurring, morebetween the comparison result indicating that the SIR measurement valueis more than the SIR reference value and the comparison resultindicating that the SIR measurement value is less than the SIR referencevalue. However, when the moving speed of the mobile station 200 is equalto or more than a predetermined value, since there is a high possibilitythat the propagation environment of the downlink radio channel changesfor a large amount during a short period, the majority decision circuit230 shortens the second predetermined period. Further, when the movingspeed of the mobile station 200 is less than the predetermined value,since there is a low possibility that the propagation environment of thedownlink radio channel changes for a large amount during a short period,the majority decision circuit 230 elongates the second predeterminedperiod.

According to the fifth embodiment described above, the same as in thethird embodiment, the mobile station 200 can increase the frequency oftransmitting the transmission parameter value when the moving speed ofthe mobile station 200 is high and there is a high possibility that thepropagation environment of the downlink radio channel changes for alarge amount during a short period, while it can reduce the frequency oftransmitting the transmission parameter value when the moving speed ofthe mobile station 200 is low and there is a low possibility that thepropagation environment of the downlink radio channel changes for alarge amount do within a short period. Thereby, the mobile station 200can transmit the transmission parameter value with a suitable frequencyin response to a fluctuation of the propagation environment of thedownlink radio channel.

FIG. 8 shows a configuration example of a mobile communication systemaccording to a sixth embodiment of the present invention. In the mobilecommunication system shown in FIG. 8, the decoder 210 and the referencevalue setting part 226 are connected with one another in the mobilestation 200, in comparison to the mobile communication system shown inFIG. 7.

In the sixth embodiment, the decoder 210 applies a decoding methodcorresponding to the encoding method applied by the encoder 102 of thebase station 100, decodes the input encoded data, and determines whetheror not data reception is succeeded in. The decoder 210 outputs an ACKsignal to the reference value setting part 226 when the data receptionhas been succeeded in. On the other hand, the decoder 210 outputs a NACKsignal to the reference value setting part 226 when the data receptionhas been failed in.

When the ACK signal is successively input during a third predeterminedperiod, the reference value setting part 226 lowers the SIR referencevalue. When the SIR reference value is thus lowered, a possibility thatthe comparison part 228 and the majority decision circuit 230 derive thecomparison result indicating that the SIR measurement value is largerthan the SIR reference value increases. Accordingly, a possibility thatthe transmission parameter determination part 214 changes the codingrate to a larger one or changes the transmission method into oneapplying smaller transmission energy per bit increases. Thus, it ispossible to improve the transmission efficiency of the downlink radiochannel in response to goodness in the propagation environment.

On the other hand, when the NACK signal is successively input during thethird predetermined period, the reference value setting part 226 raisesthe SIR reference value. When the SIR reference value is thus raised, apossibility that the comparison part 228 and the majority decisioncircuit 230 derive the comparison result indicating that the SIRmeasurement value is less then the SIR reference value increases.Accordingly, a possibility that the transmission parameter determinationpart 214 changes the coding rate to a smaller one or changes thetransmission method into one applying larger transmission energy per bitincreases. Thus, it is possible to improve the transmission quality ofthe downlink radio channel in response to badness in the propagationenvironment.

FIG. 9 shows a configuration example of a mobile communication systemaccording to a seventh embodiment of the present invention. In themobile communication system shown, in comparison to the mobilecommunication system shown in FIG. 8, a ratio deriving part 234 is newlyincluded between the decoder 210 and the reference value setting part226 in the mobile station 200.

In this seventh embodiment, the ratio deriving part 234 derives a ratiobetween the ACK signals and the NACK signals output from the decoder 210during the third predetermined period, and outputs it to the referencevalue setting part 226.

When the ratio of the ACK signals is equal to or more than apredetermined value, or when the ratio of the NACK signals is less thana redetermined value, the reference value setting part 226 lowers theSIR reference value. When the SIR reference value is thus lowered, as inthe sixth embodiment, a possibility that the transmission parameterdetermination part 214 changes the coding rate to a larger one orchanges the transmission method into one applying smaller transmissionenergy per bit increases. Thus, it is possible to improve thetransmission efficiency of the downlink radio channel.

On the other hand, when the ratio of the ACK signals is less than apredetermined value, or when the ratio of the NACK signals is equal toor more than a predetermined value, the reference value setting part 226raises the SIR reference value. When the SIR reference value is thusraised, as in the sixth embodiment, a possibility that the transmissionparameter determination part 214 changes the coding rate to a smallerone or changes the transmission method into one applying largertransmission energy per bit increases. Thus, it is possible to improvethe transmission quality of the downlink radio channel.

FIG. 10 shows a configuration example of a mobile communication systemaccording to an eighth embodiment of the present invention. In themobile communication system shown, in comparison to the mobilecommunication system shown in FIG. 9, the moving speed detection part232 and the ratio deriving part 234 are connected with one another inthe mobile station 200.

In this eighth embodiment, the same as in the seventh embodiment, theratio deriving part 234 derives a ratio between the ACK signals and theNACK signals output by the decoder 210 during the third predeterminedperiod, and outputs it to the reference value setting part 226. However,when the moving speed of the mobile station 200 is equal to or more thana predetermined value, since there is a high possibility that thepropagation environment of the downlink radio channel changes for alarge amount during a short period, the ratio deriving part 234 shortensthe third predetermined period. Further, when the moving speed of themobile station 200 is less than the predetermined value, since there isa low possibility that the propagation environment of the downlink radiochannel changes for a large amount during a short period, the ratioderiving part 234 elongates the third predetermined period.

According to the eighth embodiment described above, the mobile station200 can increase the frequency of transmitting the transmissionparameter value when the moving speed of the mobile station 200 is highand there is a high possibility that the propagation environment of thedownlink radio channel changes for a large amount during a short period,while it can reduce the frequency of transmitting the transmissionparameter value when the moving speed of the mobile station 200 is lowand there is a low possibility that the propagation environment of thedownlink radio channel changes for a large amount during a short period.Thereby, the mobile station 200 can transmit the transmission parametervalue with a suitable frequency in response to a fluctuation of thepropagation environment of the downlink radio channel.

FIG. 11 shows a configuration example of a mobile communication systemaccording to a ninth embodiment of the present invention. In the mobilecommunication system shown in FIG. 11, in comparison to the mobilecommunication system shown in FIG. 2, the TPC bit generation part 212 isnot provided between the demodulation part 208 and the transmissionparameter determination part 213, while a moving speed detection part236 and a counter 238 are provided, in the mobile station 200. Thecounter 238 is connected with the decoder 210.

In this ninth embodiment, the decoder 210 in the mobile station 200determines whether or nor data reception is succeeded in, as in thesixth embodiment. Further, the decoder 210 outputs an ACK signal to thereference value setting part 226 when data reception has been succeededin. The decoder 210 outputs a NACK signal to the reference value settingpart 226 when data reception has been failed in

The counter 238 counts the number of ACK signals and NACK signals outputfrom the decoder 210 during a fourth predetermined period, and outputsit to the transmission parameter determination part 214. However, whenthe moving speed of the mobile station 200 is equal to or more than apredetermined value, since there is a high possibility that thepropagation environment of the downlink radio channel changes for alarge amount during a short period, the counter 238 shortens the fourthpredetermined period. Further, when the moving speed of the mobilestation 200 is less than the predetermined value, since there is a lowpossibility that the propagation environment of the downlink radiochannel changes for a large amount during a short period, the counter238 elongates the fourth predetermined period.

The transmission parameter determination part 214 determines the codingrate and the modulation method which are the transmission parametersbased on the input counter value. Specifically, when the ratio of theACK signals is equal to or more than a predetermined value or the ratioof the NACK signals is less than a predetermined value, the transmissionparameter determination part 214 changes the coding rate to a larger oneor changes the modulation method to one applying smaller transmissionenergy per bit. On the other hand, when the ratio of the ACK signals isless than a predetermined value or the ratio of the NACK signals isequal to or more than a predetermined value, the transmission parameterdetermination part 214 changes the coding rate to a smaller one orchanges the modulation method to one applying larger transmission energyper bit.

In the above-described ninth embodiment, the mobile station 200generates the new transmission parameters based on whether or not datareception has been succeeded in, and does not need to apply the blockerror rate as in the prior art. Therefore the base station 100 canrapidly change the transmission parameters in response to a fluctuationof the propagation environment of the downlink radio channel.

Further, according to the ninth embodiment, the mobile station 200 canincrease the frequency of transmitting the transmission parameter valuewhen the moving speed of the mobile station 200 is high and there is ahigh possibility that the propagation environment of the downlink radiochannel changes for a large amount during a short period, while it canreduce the frequency of transmitting the transmission parameter valuewhen the moving speed of the mobile station 200 is low and there is alow possibility that the propagation environment of the downlink radiochannel changes for a large amount during a short period. Thereby, themobile station 200 can transmit the transmission parameter value with asuitable frequency in response to a fluctuation of the propagationenvironment of the downlink radio channel.

In the above-described embodiments, cased where the coding rate and themodulation method are applied as the transmission parameters have beendescribed. However, the present invention can also be applied for a casewhere a Rate-Matching ratio, the number of spreading codes used in CDMAcommunication or such is applied as the transmission parameter. Forexample, the mobile station 200 lowers the Rate-Matching ratio when thepropagation environment of the downlink radio channel is bad, while itraises the Rate-Matching ratio when the propagation environment of thedownlink ratio channel is good. Or, the mobile station reduces thenumber of spreading codes when the propagation environment of thedownlink radio channel is bad, while it increases the number of thespread codes when the propagation environment of the downlink radiochannel is good.

Further, in the above-described embodiments, cases where thetransmission parameters of the downlink radio channel are changed havebeen described. However, the present invention can also be applied for acase where transmission parameters of an uplink radio channel arechanged. When the transmission parameters of the uplink radio channelare changed, the mobile station should have a configuration of the basestation of the above-described embodiment, while the base station shouldhave a configuration of the mobile station of the above-describedembodiment.

1. A base station used in a radio communication system, comprising: atransmitting unit operable to transmit a signal to a receiver; and areceiving unit operable to receive control signals indicating a changingin transmission power and another transmission parameter of the basestation from the receiver which generates the control signals bymeasuring reception condition for a specific signal transmitted from thebase station.
 2. The base station according to claim 1, wherein theother transmission parameter corresponds to a modulation parameter or acoding parameter.
 3. The base station according to claim 1, wherein thespecific signal is transmitted via a specific channel.
 4. A receiverused in a radio communication system, comprising: a receiving unitoperable to receive a signal from a base station; a generator operableto generate control signals by measuring reception condition for aspecific signal transmitted from the base station; and a transmittingunit operable to transmit the control signals which indicate a changingin transmission power and another transmission parameter of the basestation.
 5. The receiver according to claim 4, wherein the othertransmission parameter corresponds to a modulation parameter or a codingparameter.
 6. The receiver according to claim 4, wherein the specificsignal is transmitted via a specific channel.